The following two problems need be overcome during the development of the amorphous alloy catalysts. One problem concerns how to increase the surface area of the amorphous alloy catalyst, so that its catalytic activity can be improved. The other problem concerns how to keep the catalyst in its amorphous state, i.e. how to enhance the thermal stability of the amorphous alloy catalyst. Numerous previous attempts have been directed toward addressing these problems.
In CN1,073,726A, an alloy containing Al, rare earth elements (RE), P, and Ni or Co or Fe was prepared by rapid quenching techniques. By alkaline leaching Al from the alloy with NaOH, a Ni/Co/Fe-RE-P amorphous alloy catalyst with high surface area up to 50-130 m.sup.2 /g was obtained. Its hydrogenation activity was higher than that of Raney Ni, which is widely used in industry. Such a catalyst exhibited the highest reactivity among all the prior art amorphous alloy catalysts reported thus far.
An ultra-fine Ni-B amorphous alloy catalyst was reported in J. Catal. 150 (1994) 434-438. This catalyst was prepared by adding a 2.5 M aqueous KBH.sub.4 solution dropwise at 25.degree. C. to an alcoholic nickel acetate solution at a concentration of 0.1 M with stirring . The resulted Ni-B catalyst was then washed with 6 ml of 8 M NH.sub.3.H.sub.2 O and subsequently with a large amount of distilled water. However, ultra-fine Ni-B amorphous alloy particles obtained in this manner exhibited poor thermal stability, although their surface area was determined as high as 29.7 m.sup.2 /g.
A Ni-P amorphous alloy catalyst deposited on silica was reported in Appl. Catal. 37 (1988 ) 339-343. This catalyst was prepared by chemical plating to deposit Ni and P onto a silica support. Such a supported Ni-P amorphous alloy catalyst exhibited not only a high surface area (up to 85 m.sup.2 /g), but also superior thermal stability over the corresponding unsupported amorphous alloy catalysts.
According to the results concerning the mechanism of formation of the Ni-B amorphous alloy obtained by chemical reduction, as reported in J. Phys. Chem. 97 (1993) 8504-8511, the reaction between the metal ion M.sup.2+ and BH.sub.4.sup.- in an aqueous solution follows the three steps given below: EQU BH.sub.4.sup.- +2H.sub.2 O=BO.sub.2.sup.- +4H.sub.2 .uparw. EQU BH.sub.4.sup.- +2M.sup.2+ +2H.sub.2 O=2M.dwnarw.+BO.sub.2.sup.- +4H.sup.+ +2H.sub.2 .uparw. EQU BH.sub.4.sup.- +H.sub.2 O=B+OH.sup.- +2.5H.sub.2 .uparw.
Since all of these three reactions proceed very rapidly, efficient deposition of the resulting Ni-B amorphous alloy on the support could not be guaranteed when chemical plating is carried out by mechanically mixing the support and the plating solution, nor could the homogeneous distribution of Ni-B amorphous alloy on the support be assured. Therefore, the deposition of a Ni-B amorphous alloy on the support becomes a difficult problem in this field.
Another way to improve the reactivity and/or thermal stability of the catalysts is achieved by introducing metal additives into an amorphous alloy, which has been reported widely elsewhere.
It was reported by Baoning Zong et al. in Physica Chinica Acta 9 (1993) 325 that by introducing groups IIIB or rare earth elements (abbreviated RE), such as Y, Ce and Sm, the resulted unsupported Ni-RE-P amorphous alloy catalysts exhibited a much better thermal stability over the corresponding Ni-P amorphous alloy catalyst. Similar results were also obtained by introducing La instead of the above rare earth elements, as reported in J. Chem. Soc., Faraday Trans. I 82 (1986) 702.
The effects of metal additives, such as Pd, Co, Cu, or Fe, on the hydrogenation properties of the unsupported Ni-B amorphous alloy catalysts were studied by Bingshi Li, as reported in Petrochemical Technology 23 (1994) 791. These results demonstrated that the addition of Pd could promote the activity of the Ni-B amorphous alloy catalyst for cyclopentadiene hydrogenation, while other metal additives including Co, Cu and Fe cause the reduction of hydrogenation activity.
Up to now, although various attempts have been made to improve both the reactivity and thermal stability of the amorphous alloy catalysts, unfortunately, no catalysts reported thus far can match the Ni-RE-P amorphous alloy catalyst with respect to its high surface area as described in CN 1,073,726A, or with respect to their catalytic activity.